Generation of Novel Genetic Tools to Study Cellular Heterogeneity in Adipose Tissues Much attention has been dedicated over recent years towards developing a better understanding of the cell types critically involved in maintaining energy homeostasis. In preclinical settings, the ability to direct the expression of Cre recombinase to specific tissues has been a major advance. An additional advance was made when these Cre-based recombination events were made inducible, with Cre activity temporally and spatially controlled in adult animal models. The two investigators involved in this proposal (Gupta and Scherer) have been at the forefront of the generation of mouse models now widely used in the metabolism field, exploiting in each case the expertise in their respective cell types of interest in different adipose tissues. The same two investigators now propose to take the adipose tissue- and cell type specific gene manipulation to the next level. With single cell sequencing approaches becoming more commonplace and widely used, it is increasingly obvious that a vast degree of cellular heterogeneity exists, even in cellular populations that were long considered homogeneous. There is strong evidence that such heterogeneous gene expression patterns reflect important functional differences, particularly in the areas of pre-adipocytes and adipocytes. We propose the development of novel genetic tools to study cellular heterogeneity in adipose tissues. Using ?Split-Cre? methodology, we will coordinate efforts to direct enzymatic Cre activity to specific subsets of cellular populations in different adipose tissues. This application builds upon existing gene expression databases generated by the two investigators, and proposes to expand the efforts in finding additional unique or highly enriched markers in the respective adipose depots and the cellular subpopulations. We will leverage our collective expertise and institutional infrastructure to validate the efficacy and specificity of the proposed mouse strains. These mouse models generated will constitute a new community resource and will benefit all adipose tissue physiologists in the general field of energy metabolism. As an additional step to demonstrate proof-of- concept and efficacy of these new models, we will use these newly generated mice to underline the physiological relevance of selected subpopulations of cells. These mouse models generated under the auspices of this application will constitute a new resource that will be made available to the community at large in a manner similar to what we have done with our previously generated genetic tools, along with detailed phenotypic data, expression data, and all other information of relevance, to allow for efficient and widespread use of these new tool mice.